The storing and playing back of multimedia items of information (video, audio, data, and control items of information) on digital storage media is one of the most important functions in a multimedia electronic mail system, also called an electronic multimedia mail system. In a multimedia electronic mail system, each subscriber is provided with a separate electronic mail compartment (called a mailbox), in which messages sent by other mail subscribers are deposited as multimedia mail messages. Each subscriber can fetch the separate multimedia mail from his mail compartment at any time.
The electronic mail compartments are installed on large digital mass memories. Although the capacity of storable items of information on digital storage media is constantly growing, the large quantity of data of multimedia items of information continues to present a massive storage problem.
In relation to the known methods, the present inventive method leads to a substantially higher compression and to a more effective multiplexing of multimedia data streams in a multimedia electronic mail system (see Table 1).
In contrast, the method known as MPEG-1 (ISO/IEC 11172), with 1.5 Mbit/s, requires about 11 Mbytes of memory space for the storing of a multimedia message of one minute. Seen from the perspective of memory volume, the currently known methods for multimedia electronic mail are hardly suitable in practice.
TABLE 1 ______________________________________ Examples for the storage of multimedia mail messages Playback time with 512 kbit/s non-ime with 128time standard kbit/s non- ITU-R 601 (720 .times. 576) (360 .times. 288) image image0 .times. 144) resolution of resolution of H.263; G.728, H.263;tion of G.729; G.722 H.263; audio; G.723.1; 64 G.728; G.729 ISO/IEC Medium (Mbytes): kbit/s audio audio 11172-3 ______________________________________ Hard disk/ -- about 240 about 1 about 4 minute Mbyte/min Mbyte/min (average for a mul- timedia mail message Sample 1,000 about 4,000 about 1,000 about 250 MM hard disk: MM messages messages ______________________________________
A further advantage of inventive video and audio methods in relation to the known methods is that they relate to "symmetrical real-time compression/decompression methods." The symmetry holds both for the complexity of the coder, or, respectively, of the decoder, and for the time characteristic of the coding and decoding (i.e., the complexity of the coder and of the decoder are approximately equal, or, respectively, the time expense for the coding and decoding are also approximately equal and isochronous).
The quality of the MPEG-1 video and of the MPEG-1 audio is indeed better than that of the methods listed in Table 1, but what are thereby concerned are asymmetrical methods, which require a tedious and complicated coding. The only advantage lies in the simpler decoding. However, there are numerous applications in which a reduced video and audio quality is entirely sufficient (e.g., multimedia mail, video images with head and shoulders), in which, however, a real-time coding/decoding is required, with approximately equal coding/decoding complexity.
In the present invention, a terminal for electronic multimedia mail, an ITU-T H.324 videotelephone apparatus is proposed (FIG. 1). An advantage of the videotelephone terminal is that it already contains elements of the system, such as for example audio codec, video codec, multimedia multiplexer, multimedia control, which can be of benefit to the electronic multimedia mail system. It is true that the H.324 videotelephone is tailored to a GSTN, thus to an analog telephone network. However, the invention can also be used on other networks, in particular mobile communication networks and ISDN networks. For the terminal access to the electronic multimedia mail system, in the H.324 videotelephone an additional data channel is opened, in addition to the control channel for video, speech and H.245 videotelephone. This data channel serves for controlling and communication between the terminal of the electronic multimedia mail system and the electronic mail system. In this data channel, e.g. the X.400 commands or, respectively, the X.500 commands are exchanged, using X.400 protocols and X.500 protocols, and the electronic multimedia mail system is operated.
After the connection setup between a terminal and the multimedia electronic mail system, both terminal units must mutually indicate (e.g. using ITU-T H.245) whether the one videotelephone is at the same time also a terminal for the multimedia electronic mail system, and whether the other terminal unit is the multimedia electronic mail system. If yes, then, using ITU-T H.245, either an additional data channel is opened for the operation of the multimedia electronic mail system, or in the audio channel the controlling of the multimedia electronic mail system is controlled using audible DTMF signals.
Via this data channel, the selection (login of the user) to the electronic mail system and the inputting of the password is actuated from the terminal.
If the user of the electronic mail is accepted by the system as authorized for access, he can carry out various mail system functions, e.g., querying the separate electronic mail compartment for new multimedia items of information, and fetching these if any such are present.
During fetching, the electronic mail system is the transmitter. The required multimedia channels are also selected and controlled for this purpose using a method according to H.245. The receiving multimedia terminal (videotelephone) isochronously indicates, e.g., the video image, and outputs the associated speech information.
During the sending out of a multimedia message, the required multimedia channels are opened in the separate multimedia control channel using a procedure according to ITU-T H.245. Subsequently, the address of the addressee is input into the separate control channel for the multimedia electronic mail. Next, the videotelephone terminal serves as an input means for the multimedia electronic mail. As a rule, a camera takes the picture, a microphone records the sound or, respectively, the voice of the speaker, and the H.223 multiplexer assembles the video and audio items of information. The multimedia electronic mail system stores the multimedia mail in the desired mail compartment of the addressee.
Dependent on the individual embodiments and special features, the invention preferably makes use of the following information technology standards and/or communication technology standards:
The present standardization in the ITU-T of speech coders with very low bit rates for videotelephony (ITU-T G.723) in the public telephone dialing network (GSTN) leads to qualitatively good speech coders (approximating the quality of the CCITT G.726 recommendation) with transmission speed of 5.3-6.3 kbit/s. The ITU-T G.729 speech coder also enables a digital speech transmission with a speed of 8 kbit/s. In the future, a 4 kbit/s coder will also be standardized (ITU-T G.4 kbit/s). PA1 The present standardization in the ITU-T of moving image coders with very low bit rates, e.g. for videotelephony in the public telephone dialing network (ITU-T H.263), leads to qualitatively good (QCIF resolution (180.times.144) and lower) moving image coders with the necessary transmission speed of 8-24 kbit/s or a still higher transmission speed, which require a secured type of transmission (e.g., with ITU-T H.223). An increase of the image resolution over the values defined in the standard, e.g. to CIF (360.times.288) or ITU-T 601 (720.times.576), enables the transmission of moving images with television studio quality or, respectively, with digital studio quality. PA1 The present ITU-T standardization of multiplexers (ITU-T H.223) of the audiovisual information types with very low bit rates, e.g. for videotelephony in the public telephone dialing networks, with transmission speed of 9.6-32 kbit/s or higher, enables a secured type of transmission (H.223). PA1 The present ITU-T standardization (ITU-T H.245) relating to the controlling of audiovisual types of data with very low bit rates, for example for videotelephony in public telephone dialing networks, which enables a flexible allocation of up to 15 independent useful channels, respectively with audio/speech information, video information, or data information. Each channel is provided with a flexible bandwidth, which can vary arbitrarily from application to application in the running of the multimedia electronic mail application. PA1 The concluded standardization of the ITU-T for electronic mail (recommendations of the ITU-X.400 series and ITU-T X.500 series).
These and other features of the invention are discussed in greater detail below in the following detailed description of the presently preferred embodiments with reference to the accompanying drawings.